High-dose vitamin C 'doubles kidney stone risk'

They made their finding after looking at the incidence of kidney stones over 11 years in 23,355 men.

Those who took vitamin C supplements - which typically contain 1,000 milligrammes per tablet - were at twice the risk of developing the stones compared to men who took no vitamins.

Those who took the high-dose pills most regularly were at the highest risk.

But taking vitamin C as part of a multi-vitamin - which tend to contain much lower doses of the vitamin - did not raise the risk, found the researchers from the Karolinska Institute in Sweden.

Kidney stones are small crystals of waste matter that form and can block a part of the organ or the urinary tract, causing intense pain. They affect 10 to 20 per cent of men and three to five per cent of women.

According to the Department of Health, adults need just 40mg of vitamin C a day. Its advice notes that taking high doses can cause stomach pain, flatulence and diarrhoea, but it does not mention kidney stones.

While widely believed to fight off colds, recent trials have shown it has no discernable effect as a preventive agent. However, it does have a modest effect in shortening colds, if taken as a therapeutic medicine once the infection has begun.

Professor Agneta Akesson, who led the Karolinska’s study, published in the journal JAMA Internal Medicine, said: “Given that there are no well-documented benefits of taking high doses of vitamin C in the form of dietary supplements, the wisest thing might be not to take them at all, especially if you have suffered kidney stones previously.”

Dr Carrie Ruxton, from the Health Supplements Information Service, said as the study only looked at men results could not be assumed to be the same for women.

She added: "Since higher dose vitamin C - 500mg per day or more - is proven to reduce the duration of a cold orflu, it is worth taking these in the short-term when required.

"This study looked at people who were habitually taking around 1000mg several times a week.

"It is likely that short-term, sporadic use of higher dose vitamin C does not constitute a risk for kidney stones and can be helpful when people have a cold."